Printing plate making apparatus and printing plate making method

ABSTRACT

A printing plate making apparatus which scans a recording medium by light beam in a predetermined pixel pitch, thereby engraving a surface of the recording medium to make a printing plate, wherein an upper surface of a convex portion of light power of the light beam engraving all or part of an adjacent region which is adjacent to a convex portion which is to be left in a convex shape on a surface of the recording medium is set to an threshold engraving energy or less, and light power of light beam in a vicinity region in vicinity of outer side of a region defined as the adjacent region is brought higher than light power in the adjacent region.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplications Nos. 2008-058160, 2008-058159, and 2009-009055, thedisclosures of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printing plate making apparatus and aprinting plate making method.

2. Description of the Related Art

There is known a printing plate making apparatus including a drum beingprovided at its outer peripheral surface with a recording plate(recording medium) and being rotated in a horizontal scanning direction,and a two-dimensional image on the recording plate being engraved t(recorded) on the recording plate by scanning the recording medium in avertical scanning direction that is perpendicular to the horizontaldirection with a laser beam in accordance with image data of an imagethat is to be engraved.

In the above printing plate making apparatus, when a relief printingplate such as a flexographic printing plate and an intaglio printingplate such as a gravure is directly engraved by laser beam, it isrequired to satisfy both reproducibility of fine line or mesh point inshallow engraving (precision engraving) when engraving a narrow regionand deep engraving (rough engraving) when engraving a wide region.

Since it is generally difficult to satisfy both two requirements at thesame time, there is known a method in which laser beam having a smallspot diameter for shallow engraving (precision engraving) and high powerlaser beam for deep engraving (rough engraving) are provided, andengraving is carried out using these laser beams separately (e.g., U.S.Pat. No. 6,150,629, U.S. Patent Application Laid-Open No.2006/0279794A1, and Japanese Patent Application Laid-Open (JP-A) No.2005-224481).

When printing is carried out using a relief printing plate such as aflexographic printing plate, if an edge shape of a convex portion formedon the plate is obtuse or a foundation which supports the convex portionis weak, printing density is varied by a pressing force against aprinting medium, fine line or highlight point is not clearly printed orclear print is not carried out in some cases.

To reduce these problems, it is proposed to form a region remaining inconvex shape such that a convex portion having rectangular cross sectionis formed on top of a foundation having a trapezoidal cross section (seeJP-A No. 6-234262). To directly engraving a relief printing plate bylaser beams at a higher speed, it is proposed to engrave a recordingmedium by exposing the recording medium to a light twice (see JapanesePatent No. 35562044).

SUMMARY OF THE INVENTION

However, it is required to engrave a recording plate more precisely. Inaddition, when a recording medium is engraved by scanned twice, in orderto print clearly, it is required to make a shape of a region which is tobe left in convex shape to a shape wherein a convex portion havingrectangular cross section is formed on top of a foundation having atrapezoidal cross section.

The object that is to be achieved by the present invention is to solvethe above problem.

A first aspect for achieving the above object relates to a printingplate making apparatus which scans a recording medium with a light beamat a predetermined pixel pitch, thereby engraving a surface of therecording medium to make a printing plate, wherein a light power of thelight beam, which engraves all or part of a region which is adjacent toa convex portion which is to be left in a convex shape on a surface ofthe recording medium, is equal or less than a threshold engravingenergy, and at a vicinity region in the vicinity of an outer side of theadjacent region, the light power of the light beam is increased to alevel higher than the light power used in the adjacent region.

According to the printing plate making apparatus of the first aspect,the light power of the light beam emitted to all or part of the adjacentregion which is adjacent to the convex portion in which the surface ofthe recording medium is to be left in a convex shape is reduced suchthat the exposure light of the light beam on the upper surface of theconvex portion is equal or less than the threshold engraving energy.Accordingly, engraving on the upper surface of the convex portion isprevented or suppressed. Thus, the width of the upper surface of theconvex portion may be brought closer to the desired width (desired widthis secured or substantially secured).

At the vicinity region in the vicinity of the outer side of the regionin the adjacent region where the energy is equal or smaller than thethreshold engraving energy, the light power of the light beam isincreased than the light power at the adjacent region and the engravingis carried out, and thus, the inclination angle of the side surface ofthe convex portion becomes acute. In other words, the shape of theconvex portion becomes closer to a rectangular shape.

The width of the upper surface of the convex portion may be closer tothe desired width and the shape of the convex portion becomes closer tothe rectangular shape. That is, the convex portion is preciselyengraved. Thus, reproducibility of fine line or meshed point on aprinting medium printed by a recording medium made into a plate isimproved.

By the apparatus of the first aspect, even when a diameter of light beamis large, a convex portion is engraved precisely. Even when a diameterof light beam is small, a convex portion is engraved more precisely thanwhen an apparatus that does not have the technical feature of theapparatus of the first aspect.

According to the printing plate making apparatus of the first aspect,since the width of the upper surface of the convex portion can made tobe closer to the desired width and the shape of the convex portionbecomes closer to the rectangular shape, there is an excellent effectthat a recording medium can be precisely engraved.

The increasing amount of intensity of the light power of light beam atthe vicinity region is determined by taking into consideration the typeof the recording medium or the other.

The width of the adjacent region and the vicinity region are determinedby taking into consideration the size of the convex portion, a beamdiameter of light beam, the pixel pitch, and the type of recordingmedium or the other.

A second aspect for achieving the above object relates to the printingplate making apparatus of the first aspect, wherein the adjacent regioncomprises one pixel or more.

In the printing plate making apparatus of the second aspect, since thewidth of the adjacent region is one pixel or more, the width of theupper surface of the convex portion may be brought closer to the desiredwidth (the desired width is secured more reliably or substantiallysecured). Further, since the light power is controlled by pixel(s), itis easy to control the light power.

Therefore, the printing plate making apparatus of the second aspect hasan excellent effect that the width of the upper surface of the convexportion may be brought closer to the desired width.

A third aspect for achieving the above object relates to the printingplate making apparatus of the first or second aspect, pulse exposure iscarried out at a pulse width of one pixel or less and engraving iscarried out at the vicinity region.

In the printing plate making apparatus of the third aspect, therecording plate is pulse-exposed with a pulse width of one pixel or lessand engraved, thereby the inclination angle of the side surface of theconvex portion becomes more acute. In other words, the shape of theconvex portion is brought closer to the rectangular shape.

The pulse exposure mentioned here means control in which the light powerof light beam is turned “OFF→ON→OFF”, and the pulse width means a width(interval) during which the light power is ON.

A fourth aspect for achieving the above object relates to the thirdaspect, wherein the pulse width of the pulse exposure is 0.5 pixels orless.

In the printing plate making apparatus of the fourth aspect, since thepulse width of the pulse exposure is 0.5 pixels or less, the inclinationangle of the side surface of the convex portion becomes more acute. Inother words, the shape of the convex portion is brought closer to therectangular shape.

A fifth aspect for achieving the above object relates to the printingplate making apparatus of the third aspect, wherein the pulse width ofthe pulse exposure is 0.25 pixels or less.

In the printing plate making apparatus of the fifth aspect, since thepulse width of the pulse exposure is 0.25 pixels or less, thereby theinclination angle of the side surface of the convex portion becomes moreacute. In other words, the shape of the convex portion is brought closerto the rectangular shape.

The printing plate making apparatus of the third to fifth aspectsexhibit an excellent effect that the shape of the convex portion may bebrought closer to the rectangular shape.

A sixth aspect for achieving the above object relates to the printingplate making apparatus of any one of the first to fifth aspects, whereinthe light beam engraving the recording medium is focused by an imaginglens after being emitted from a fiber array light source.

In the printing plate making apparatus of the sixth aspect, after thelight beam is emitted from the fiber array light source, the light beamis focused by an imaging lens to engrave the recording medium.Therefore, as compared with an expensive light source such as a fiberlaser and CO₂ laser, the cost of the printing plate making apparatus maybe reduced.

Nevertheless, the width of the upper surface of the convex portion maybe brought close to the desired width and the shape of the convexportion may be brought close to the rectangular shape. That is, thereproducibility of fine lines or meshed points on a printing mediumprinted by a recording medium after being engraved by light beamscanning may be improved.

According to the printing plate making apparatus of the sixth aspect,there is an excellent effect that cost may be reduced compared with aprinting plate making apparatus having an expensive light source such asa fiber laser.

A seventh aspect for achieving the above object relates to a printingplate making method, the method comprising scanning a recording mediumby light beam by a predetermined pixel pitch, thereby engraving asurface of the recording medium to make a printing plate, wherein alight power of the light beam engraving all or part of an adjacentregion which is adjacent to a convex portion which is to be left in aconvex shape on a surface of the recording medium is reduced to so as tobe equal to or less than a threshold engraving energy, and the lightpower of a light beam for engraving a region in the vicinity of an outerside of the adjacent region is increased to a value higher than thelight power used in the adjacent region.

According to the printing plate making method of the seventh aspect, thewidth of the upper surface of the convex portion may be brought close tothe desired width and the shape of the convex portion may be broughtclose to the rectangular shape. Therefore, the convex portion isprecisely engraved. Thus, the reproducibility of fine lines or meshedpoints on a printing medium printed by a recording medium that is madeinto a printing plate is improved.

The threshold engraving energy is a light energy of a light beamrequired for engraving a surface of the recording medium, and if thelight energy is smaller than the threshold engraving energy, therecording medium is not be engraved. In other words, even if therecording medium is exposed to light beam having a light energy equal toor smaller than the threshold engraving energy, the surface of therecording medium is not engraved. The threshold engraving energy differsdepending upon the type (material) of the recording medium.

According to the seventh aspect, since the width of the upper surface ofthe convex portion may be brought close to the desired width and theshape of the convex portion may be brought close to the rectangularshape, there is an excellent effect that the recording medium isprecisely engraved.

An eighth aspect for achieving the above object relates to a printingplate making apparatus which scans a recording medium by a light beam ata predetermined pixel pitch, thereby engraving the recording medium tomake a printing plate, wherein the light beam includes a first lightbeam and a second light beam, a light power of the first light beam isdefined as P1, a light power of the second light beam is P2, and depthsengraved by the respective light powers are d1 and d2; after therecording medium is scanned by one of the light beams in a predeterminedpixel pitch to a first depth d1 or d2, a scanning line scanned by theone light beam is scanned by the other light beam; and the recordingmedium is engraved to a second depth d1+d2 which is deeper than thefirst depth.

An upstream end of a convex portion constituting an upper portion of aregion where the recording medium is to be left in a convex shape isdefined as an upstream reference position; light power control of thefirst light beam is carried out such that when the recording medium isscanned at a predetermined pixel pitch with the first light beam, from afirst point separated away from the upstream reference position by mpixels upstream in the scanning direction or the vicinity thereof, to asecond point which is separated away from the upstream referenceposition on the surface of the recording medium downstream in thescanning direction by n pixels, a light power of the first light beam isreduced linearly or substantially linearly from P1 so that at theupstream reference position or the vicinity thereof the light power ofthe first light beam is equal to or less than a threshold engravingenergy. When the recording medium is scanned by the second light beam ata predetermined pixel pitch to engrave, from a third point separatedaway from the upstream reference position in the upstream in thescanning direction by (2m+n)×(P2/P1) pixels or the vicinity thereof, thelight power of the second light beam is reduced linearly orsubstantially linearly from P2 such that it becomes the thresholdengraving energy or less at the first point or the vicinity thereof.

According to the printing plate making apparatus of the eighth aspect,when scanning the recording medium by the first light beam at thepredetermined pixel pitch and engraving at the first depth, from thefirst point that is a point separated away from the upstream referenceposition upstream in the scanning direction by m pixels or the vicinitythereof along the line segment connecting the first point in the firstdepth and the second point that is a point separated away from theupstream reference position in the surface of the recording mediumdownstream in the scanning direction by n pixels, the light power of thefirst light beam is reduced linearly or substantially linearly from P1,and the energy is set to be equal to or less than the thresholdengraving energy at the upstream reference position or the vicinitythereof.

When the recording medium is scanned by the second light beam in thepredetermined pixel pitch and engraved at the second depth, the lightpower of the second light beam is reduced linearly or substantiallylinearly from P2 along the line segment connecting the first point andthe third point which is separated away from the upstream referenceposition upstream in the scanning direction by (2m+n)×(P2/P1) pixels orthe vicinity thereof, and the energy is set to be equal to or less thanthe threshold engraving energy at the first point or the vicinitythereof.

By controlling the light power in the above described manner, the convexportion having a substantially rectangular cross section is formed ontop of a foundation having a substantially trapezoidal cross sectionupstream in the scanning direction of the region which is to be left ina convex shape. For example, an inclined surface which is engraved bythe second light beam is substantially straightly connected to aninclined surface of the foundation having the trapezoidal cross sectionupstream in the scanning direction when it is engraved by the firstlight beam.

Therefore, even if the recording medium is engraved by scanning twiceand, the cross section shape of the region which is to be left in aconvex shape may be brought close to a shape that a convex portionhaving a substantially rectangular cross section is formed on top of afoundation having a substantially trapezoidal cross section.

Accordingly, deviation of printing density in accordance with a pressureapplied from a recording medium that is made into a printing plate (aprinting plate) to a printing medium and failure of clearly printing afine line or a high light point are prevented or suppressed, andtherefore, clear printing can be carried out.

According to the printing plate making apparatus of the eighth aspect,when the recording medium is engraved by scanning twice, the shape ofthe region which is to be left in a convex shape may be brought close toa shape such that a convex portion having a substantially rectangularcross section is formed on top of a foundation having a substantiallytrapezoidal cross section.

A ninth aspect for achieving the above object relates to the printingplate making apparatus of the eighth aspect, wherein when engraving allor part of an adjacent region which is adjacent upstream in the scanningdirection to a convex portion forming an upper portion of a region wherea surface of the recording medium is to be left in a convex shape, alight power of the first light beam is reduced so as to be equal to orless than the threshold engraving energy, at the upper surface of theconvex portion, and in a vicinity region which is in the vicinity of anouter side of an upstream side of the adjacent region in the scanningdirection, the light power of the first light beam is set higher thanthe light power of the first beam when engraving along a line segmentconnecting the first point and the second point.

In the printing plate making apparatus of the ninth aspect, the lightpower of the first light beam emitted to all or part of the adjacentregion which is adjacent to the convex portion upstream in the scanningdirection is reduced such that the exposure of the light beam to theupper surface of the convex portion is carried out at an intensity equalto or less than the threshold engraving energy. Accordingly, engravingthe upper surface of the convex portion is prevented or suppressed.Thus, the width of the upper surface of the convex portion is broughtcloser to the desired width.

At the vicinity region which is adjacent to the outer side upstream inthe scanning direction of the region in the adjacent region where alight energy is set to be equal to or less than the threshold engravingenergy, the region is engraved while increasing the light power of thefirst light beam higher than the light power of the first light beamwhen engraving along the line segment connecting the first point and thesecond point. Accordingly, the inclination angle of the side surface ofthe convex portion becomes acute. In other words, the shape of theconvex portion becomes close to the rectangular shape.

Accordingly, the width of the upper surface of the convex portion formedon top of the foundation having a substantially trapezoidal crosssection is brought close to the desired width, and the shape of theconvex portion becomes close to the rectangular shape. That is, theconvex portion is engraved precisely. Thus, the reproducibility of fineline or meshed point on a printing medium printed by a recording mediummade into a printing plate is improved.

According to the printing plate making apparatus of the tenth aspect,the shape of the cross section of a convex portion formed on top of afoundation having a substantially trapezoidal cross section may bebrought closer to the rectangular shape.

An eleventh aspect for achieving the above object relates to a printingplate making apparatus which scans a recording medium by a light beam ata predetermined pixel pitch, thereby engraving a surface of therecording medium to make a printing plate, wherein: the light beamincludes a first light beam and a second light beam, a light power ofthe first light beam is P1, a light power of the second light beam isP2, and depths engraved by the respective light powers are d1 and d2;after scanning the recording medium with one of the light beams at apredetermined pixel pitch to engrave the recording medium to a firstdepth d1 or d2, a scanning line scanned by the one light beam is scannedby the other light beam and the recording medium is engraved to a seconddepth d1+d2 which is deeper than the first depth; a downstream end of aconvex portion forming an upper portion of a region where the recordingmedium is to be left in a convex shape downstream in the scanningdirection is defined as a downstream reference position; light powercontrol of the light beam is carried out such that, when the recordingmedium is scanned at a predetermined pixel pitch with the first lightbeam, the light power of the first light beam is set to be equal to orgreater than the threshold engraving energy at the downstream referenceposition or the vicinity thereof; from a fifth point separated from thedownstream reference position downstream in the scanning direction by mpixels to a sixth point on a surface of the recording medium separatedfrom the downstream reference position in the scanning direction by npixels, the light power of the first light beam is increased linearly orsubstantially linearly, and is set to P1 at the fifth point or thevicinity thereof; and when the recording medium is scanned at apredetermined pixel pitch by the second light beam, a light power of thesecond light beam is equal to or greater than the threshold engravingenergy at the fifth point or the vicinity thereof, and towards a seventhpoint separated from the fifth point and the downstream referenceposition downstream in the scanning direction by (2m+n)×(P2/P1) pixels,the light power is increased linearly or substantially linearly and setto P2 at the seventh point or the vicinity thereof.

According to the printing plate making apparatus of the eleventh aspect,when scanning the recording medium by the first light beam at apredetermined pixel pitch, thereby engraving the recording medium at afirst depth, the light power of the first light beam is set so as to beequal or lower than the threshold engraving energy, and then, from thedownstream reference position or the vicinity thereof the light power isincreased linearly or substantially linearly along the line segmentconnecting the fifth point at the first depth which is separated fromthe downstream reference position downstream in the scanning directionby m pixels and the sixth point in the surface of the recording mediumwhich is separated away from the downstream reference position upstreamin the scanning direction by n pixels, and the light power is set to P1at the fifth point or the vicinity thereof.

When scanning the recording medium by the second light beam at apredetermined pixel pitch and engraving the recording medium at a seconddepth, the light power of the second light beam is set so as to be equalor higher than the threshold engraving energy, from the fifth point orthe vicinity thereof and then, the light power is increased linearly orsubstantially linearly along the line segment connecting the fifth pointand the seventh point at the second depth separated away from thedownstream reference position downstream in the scanning direction in(2m+n)×(P2/P1) pixels, and the light power is set to P2 at the seventhpoint or the vicinity thereof.

By controlling the light power in this manner, a convex portion having asubstantially rectangular cross section is formed on top of a foundationhaving a substantially trapezoidal cross section downstream in thescanning direction of the region which is to be left in a convex shape.For example, an inclined surface which is engraved by the second lightbeam is substantially straightly connected to an inclined surface of thefoundation having the trapezoidal cross section downstream in thescanning direction when it is engraved by the first light beam.

Therefore, even if the recording medium is engraved by scanning twice,the cross section shape of the region which is to be left in a convexshape may be brought close to a shape such that a convex portion havingthe substantially rectangular cross section is formed on top of afoundation having a substantially trapezoidal cross section.

Accordingly, for example, it can be prevented or suppressed thatdeviation of pressing force applied from a recording medium made into aprinting plate to a printing medium causes printing density deviationand that fine lines or highlight points are not printed clearly, andtherefore, clear printing may be carried out.

According to the printing plate making apparatus of the eleventh aspect,when the recording medium is engraved by scanning twice, the shape ofthe region which is to be left in a convex shape may be brought closeinto such a shape that a convex portion having a substantiallyrectangular cross section is formed on top of a foundation having asubstantially trapezoidal cross section.

A twelfth for achieving the above object relates to the printing platemaking apparatus of the eleventh aspect wherein a light power of thefirst light beam, which engraves all or part of an adjacent region whichis adjacent to a convex portion downstream in the scanning direction ofthe convex portion which forms an upper portion of a region where asurface of the recording medium is to be left in a convex shape, isreduced so as to be equal or smaller than the value of the thresholdengraving energy; at the upper surface of the convex portion, and in thevicinity region in vicinity of an outer side of an adjacent regionupstream in the scanning direction, light power of the first light beamis increased higher than the light power of the first light beam whenengraving along a line segment connecting the fifth point and the sixthpoint.

According to the printing plate making apparatus of the twelfth aspect,the light power of the first light beam emitted to all or a part of theadjacent region which is adjacent to the downstream in the scanningdirection of the convex portion constituting the upper portion of theregion where the surface of the recording medium is left in a convexshape is reduced such that the exposure of the light beam emitted to theupper surface of the convex portion becomes to be equal or less than thethreshold engraving energy. Accordingly, engraving of the upper surfaceof the convex portion is prevented or suppressed. Thus, the width of theupper surface of the convex portion is brought closer to the desiredwidth.

At the vicinity region which is in the vicinity of the outer sidedownstream in the scanning direction of the region in the adjacentregion where the light energy is equal to or less than the thresholdengraving energy, the region is engraved while increasing the lightpower of the first light beam as compared with the light energy whenengraving along the line segment connecting the fifth point and thesixth point. Thus, the inclination angle of the side surface of theconvex portion becomes acute. In other words, the shape of the convexportion becomes close to the rectangular shape.

Consequently, the width of the upper surface of the convex portionformed on top of the foundation having a substantially trapezoidal crosssection is brought close to the desired width, and the shape of theconvex portion becomes close to the rectangular shape. That is, theconvex portion is engraved precisely. Thus, the reproducibility of finelines or meshed points on a printing medium printed by a recordingmedium made into a printing plate is improved.

According to the printing plate making apparatus of the twelfth aspect,the shape of a cross section of a convex portion formed on top of afoundation having a substantially trapezoidal cross section may bebrought closer to the rectangular shape.

A thirteenth aspect for achieving the above object relates to theprinting plate making apparatus of any one of the eighth to twelfthaspects, wherein n is an integer from 1 to 3.

In the printing plate making apparatus of the thirteenth aspect, sincethe n is an integer from 1 to 3, the convex portion having thesubstantially rectangular cross section is formed to an appropriateheight.

Thus, according to the printing plate making apparatus, the convexportion having the substantially rectangular cross section may be formedto an appropriate height.

According to a fourteenth aspect for achieving the above object relatesto the printing plate making apparatus of any one of the eighth tothirteenth aspects wherein m is an integer from 5 to 30.

According to the printing plate making apparatus of the fourteenthaspect, since m is an integer from 5 to 30, the foundation having asubstantially trapezoidal cross section is formed to an appropriatewidth.

According to the printing plate making apparatus of the fourteenthaspect, the foundation having a substantially trapezoidal cross sectionmay be formed to the appropriate width.

A fifteenth aspect for achieving the above object relates to theprinting plate making apparatus of any one of the eighth to fourteenthaspects, wherein the recording medium scanned by light beam in ahorizontal scanning direction and a vertical scanning direction that isperpendicular to the horizontal direction, and light power control ofthe light beam is carried out when the recording medium is scanned atone or both of the horizontal scanning direction and vertical scanningdirection.

According to the printing plate making apparatus of the fifteenthaspect, the recording medium is scanned by the light beam in thehorizontal scanning direction and the vertical scanning directionperpendicular to the horizontal scanning direction. Consequently, theregion which is to be left in a convex shape is formed into thesubstantially rectangular shape as viewed from above. On at least oneside of the substantially rectangular shape, a convex portion having asubstantially rectangular cross section is formed on top of a foundationhaving a substantially trapezoidal cross section.

Thus, according to the printing plate making apparatus, the region whichis to be left in a convex shape is formed into the substantiallyrectangular shape as viewed from the above.

A sixteenth aspect for achieving the above object relates to a printingplate making method for engraving a surface of a recording medium tomake a printing plate, the method comprising scanning a recording mediumwith a light beam at a predetermined pixel pitch, wherein a light beamincludes a first light beam and a second light beam, a light power ofthe first light beam is P1, a light power of the second light beam isP2, and depths engraved by the respective light powers are d1 and d2;after the recording medium is scanned by one of the light beams at apredetermined pixel pitch to the first depth d1 or d2, a scanning linescanned by the one light beam is scanned by the other light beam, andthe recording medium is engraved to a second depth d1+d2 which is deeperthan the first depth; an upstream end of a convex portion forming anupper portion of a region where the recording medium is to be left in aconvex shape upstream in the scanning direction is defined as anupstream reference position; light power control of the first light beamis carried out such that, when the recording medium is scanned at apredetermined pixel pitch with the first light beam, from a first pointwhich is separated from the upstream reference position by m pixels inthe scanning direction, or the vicinity thereof, to a second point onthe surface of the recording medium separated from the upstreamreference position by n pixels downstream in the scanning direction, alight power of the first light beam is reduced linearly or substantiallylinearly from P1 so that at the upstream reference position or thevicinity thereof the light power of the first light beam is equal to orless than a threshold engraving energy; and when the recording medium isscanned by the second light beam at a predetermined pixel pitch, from athird point or the vicinity thereof, the third point being separatedfrom the upstream reference position by (2m+n)×(P2/P1) pixels in thescanning direction, the light power of the second light beam is reducedlinearly or substantially linearly from P2 such that it becomes thethreshold engraving energy or less at the first point or the vicinitythereof.

According to the printing plate making method of the sixteenth aspect,by engraving a recording medium (making the plate) according to theabove manner, a convex portion having a substantially rectangular crosssection is formed on top of a foundation having a substantiallytrapezoidal cross section upstream in the scanning direction of theregion which is to be left in a convex shape. For example, an inclinedsurface which is engraved by the second light beam is substantiallystraightly connected to an inclined surface of the foundation having thetrapezoidal cross section upstream in the scanning direction when it isengraved by the first light beam.

Therefore, even if the recording medium is engraved by scanning twice,the cross section shape of the region which is to be left in a convexshape may be brought close into such a shape that the convex portionhaving the substantially rectangular cross section is formed on top ofthe foundation having a substantially trapezoidal cross section.

Thus, it can be prevented or suppressed that printing density deviationis caused by deviation of pressing force applied to a recording mediumthat is made into a printing plate to a printing medium, and that a fineline or a highlight point is not printed clearly, and accordingly, clearprinting may be carried out.

According to the printing plate making method of the sixteenth aspect,when the recording medium is engraved by scanning twice, the shape ofthe region which is to be left in a convex shape may be brought close toa shape of a convex portion having a substantially rectangular crosssection and being formed on top of a foundation having a substantiallytrapezoidal cross section.

A seventeenth aspect for achieving the above object relates to theprinting plate making method of the sixteenth aspect wherein whenengraving all or part of an adjacent region which is adjacent upstreamin the scanning direction to a convex portion forming an upper portionof a region where a surface of the recording medium is to be left in aconvex shape, a light power of the first light beam is reduced so as tobe equal to or less than the threshold engraving energy, at the uppersurface of the convex portion, and in a vicinity region which is in thevicinity of an outer side of an upstream side of the adjacent region inthe scanning direction, the light power of the first light beam is sethigher than the light power of the first light beam when engraving alonga line segment connecting the first point and the second point.

According to the printing plate making method of the seventeenth aspect,the light power of the first light beam emitted to all or a part of theadjacent region which is adjacent to the downstream in the scanningdirection of the convex portion constituting the upper portion of theregion where the surface of the recording medium is left in a convexshape is reduced such that the exposure of the light beam emitted to theupper surface of the convex portion becomes the threshold engravingenergy or less. With this, the upper surface of the convex portion isprevented or suppressed from being engraved. Thus, the width of theupper surface of the convex portion is brought closer to the desiredwidth.

At the vicinity region which is in the vicinity of the outer sideupstream in the scanning direction of the region in the adjacent regionwhere the light energy of the first light beam is equal to or less thanthe threshold engraving energy, the region is engraved while increasingthe light power of the first light beam as compared with the lightenergy of the first beam when engraving along the line segmentconnecting the first point and the second point. Thus, the inclinationangle of the side surface of the convex portion becomes acute. In otherwords, the shape of the convex portion becomes close to the rectangularshape.

Therefore, the width of the upper surface of the convex portion formedon top of the foundation having a substantially trapezoidal crosssection is brought close to the desired width, and accordingly, thesectional shape of the convex portion becomes closer to a rectangularshape. That is, the convex portion is engraved precisely. Thus, thereproducibility of fine line or meshed point on a printing mediumprinted by a recording medium made into a printing plate according tothis aspect is improved.

According to the printing plate making method, the shape of the crosssection of the convex portion formed on top of the foundation having asubstantially trapezoidal cross section may be brought closer to therectangular shape.

An eighteenth for achieving the above object relates to a printing platemaking method for engraving a surface of a recording medium to make aprinting plate, the method comprising scanning a recording medium with alight beam at a predetermined pixel pitch, wherein a light beam includesa first light beam and a second light beam, a light power of the firstlight beam is P1, a light power of the second light beam is P2, anddepths engraved by the respective light powers are d1 and d2; after therecording medium is scanned by one of the light beams at a predeterminedpixel pitch to engrave to the first depth d1 or d2, a scanning linescanned by the one light beam is scanned by the other light beam, andthe recording medium is engraved to a second depth d1+d2 which is deeperthan the first depth; an upstream end of a convex portion forming anupper portion of a region where the recording medium is to be left in aconvex shape upstream in the scanning direction is defined as anupstream reference position; when the recording medium is scanned at apredetermined pixel pitch by the first light beam, a light power of thefirst light beam is set to a threshold engraving energy or higher fromthe downstream reference position or the vicinity thereof, toward afifth point separated from the downstream reference position downstreamin the scanning direction by m pixels and toward a sixth point on asurface of the recording medium separated by n pixels from thedownstream reference position in the scanning direction, the light poweris increased linearly or substantially linearly so that the light poweris P1 at the fifth point or the vicinity thereof, when the recordingmedium is scanned by the second light beam in a predetermined pixelpitch, a light power of the second light beam is set to the thresholdengraving energy or higher from the fifth point or the vicinity thereof,and then, the light power is increased linearly or substantiallylinearly along a line segment connecting the fifth point and a seventhpoint separated away from the downstream reference position downstreamin the scanning direction by (2m+n)×(P2/P1) pixels, and the light powerof the second light beam is set to P2 at the seventh point or thevicinity thereof.

By engraving (making the plate) a recording medium according to theprinting plate making method of the eighteenth aspect, a convex portionhaving a substantially rectangular cross section is formed on top of thefoundation having a substantially trapezoidal cross section downstreamin the scanning direction of the region which is to be left in a convexshape. For example, an inclined surface which is engraved by the secondlight beam is substantially straightly connected to an inclined surfaceof the foundation having the trapezoidal cross section downstream in thescanning direction when it is engraved by the first light beam.

Therefore, even if the recording medium is engraved by scanning twice,the cross section shape of the region which is to be left in a convexshape may be brought close to a shape of convex region including afoundation having a substantially trapezoidal cross section and a convexportion having a substantially rectangular cross section is formed ontop thereof.

Thus, for example, it can be prevented or suppressed that deviation ofprinting density is caused by deviation of pressing force applied from arecording medium made into a printing plate to a printing medium andthat a fine line or highlight point is not printed clearly, and clearprinting may be carried out.

According to the printing plate making method of the eighteenth aspect,when the recording medium is engraved by scanning twice, the shape ofthe region which is to be left in a convex shape may be brought closerto a shape of a convex region including foundation having asubstantially trapezoidal cross section and a convex portion having asubstantially rectangular cross section formed on top thereof.

A nineteenth for achieving the above object relates to the printingplate making method of the eighteenth aspect wherein when engraving allor part of an adjacent region which is adjacent to a convex portiondownstream in the scanning direction forming an upper portion of aregion where a surface of the recording medium is to be left in a convexshape, a light power of the first light beam is reduced so as to beequal to or less than the threshold engraving energy, at the uppersurface of the convex portion, and at the vicinity region in thevicinity of the outer side of the adjacent region upstream in thescanning direction, a light power of the first light beam is increasedto be greater than the light energy, engraving along a line segmentconnecting the fifth point and the sixth point.

According to the printing plate making apparatus of the nineteenthaspect, the light power of the first light beam emitted to all or a partof the adjacent region which is adjacent to the downstream in thescanning direction of the convex portion constituting the upper portionof the region where the surface of the recording medium is to be left ina convex shape is reduced such that the exposure of the light beamemitted to the upper surface of the convex portion becomes the thresholdengraving energy or less. Consequently, engraving of the upper surfaceof the convex portion is prevented or suppressed. Thus, the width of theupper surface of the convex portion is brought closer to a desiredwidth.

At the vicinity region which is in the vicinity of the outer sidedownstream in the scanning direction of the region in the adjacentregion where the light energy of the first light beam is equal to orless than the threshold engraving energy or less, the region is engravedwhile increasing the light power of the first light beam as comparedwhen engraving along the line segment connecting the fifth point and thesixth point. Thus, the inclination angle of the side surface of theconvex portion becomes acute. In other words, the shape of the convexportion becomes close to the rectangular shape.

According to the method of this aspect, the width of the upper surfaceof the convex portion formed on top of the foundation having asubstantially trapezoidal cross section is brought close to the desiredwidth, and the shape of the convex portion becomes close to therectangular shape. That is, the convex portion is engraved precisely.Thus, the reproducibility of fine line or meshed point on a printingmedium printed by a recording medium made into a printing plateaccording to this method is improved.

The threshold engraving energy is a light power (a light energy) of alight beam required for engraving a surface of the recording medium, andif the light power is smaller than the threshold engraving energy, therecording medium is not be engraved. In other words, even if therecording medium is exposed to a light beam equal to or less than thethreshold engraving energy, the surface of the recording medium is notengraved. The threshold engraving energy differs depending upon the typeor the material(s) of the recording medium.

According to the printing plate making method of the nineteenth aspect,the shape of a cross section of a convex portion formed on top of afoundation having a substantially trapezoidal cross section may bebrought closer to a rectangular shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram (perspective view) of a structure showinga printing plate making apparatus according to an exemplary embodimentof the present invention.

FIG. 2 is a perspective view of a fiber array portion and optical fibersof a laser recording device.

FIG. 3 is a schematic diagram showing a light-exposing portion of thefiber array portion.

FIG. 4 is a diagram for explaining disposition positions and scanninglines of optical fiber ends.

FIG. 5 is a plan view of the printing plate making apparatus as viewedfrom above.

FIG. 6 is a block diagram showing a structure of a control system of theprinting plate making apparatus.

FIG. 7 is a flowchart showing a general outline of processing forrecording an image by a laser recording device.

FIG. 8 is a schematic explanatory diagram showing an essential portionof an exposure head and emitted laser beam.

FIG. 9A is a graph showing light power of center cross section thatshows light power control to which the invention is not applied and aspot diameter (spot shape) of laser beam when a beam diameter D is 20μm, and FIG. 9B is a schematic diagram showing light power variationwhen scanning is carried out by laser beam having the spot diameter(spot shape) shown in FIG. 9A to form a convex fine line (pixel regionto be left) of 21.2 μm.

FIG. 9C shows a pixel exposure amount signal of laser beam, FIG. 9D is agraph showing integrating energy, of light power of laser beam of crosssection taken along the A-A line in FIG. 9B, and FIG. 9E is a schematicdiagram showing a cross section shape of a convex fine line P takenalong the line A-A′ in FIG. 9B.

FIG. 10A shows light power control to which the invention is not appliedand a spot diameter (spot shape) of laser beam when a beam diameter D is20 μm, FIG. 10B is a graph showing a light power of center crosssection, FIG. 10C schematically shows light power variation whenscanning is carried out using laser beam of a spot diameter (spot shape)shown in FIG. 10A and a convex fine line (pixel region to be left) of21.2 μm is formed, FIG. 10C shows a pixel exposure amount signal oflaser beam, FIG. 10D is a graph showing integrating energy, of lightpower of laser beam of cross section taken along the A-A line in FIG.10B, and FIG. 10E schematically shows a cross section shape of a convexfine line P taken along the A-A′ in FIG. 10B.

FIG. 11A shows light power control to which the invention is applied anda pixel exposure amount signal of laser beam when beam diameter D is 20μm, FIG. 11B is a graph showing integrating energy, of light power oflaser beam of cross section taken along the line A-A in FIG. 11B, andFIG. 11C schematically shows a cross section shape of a convex fine lineP taken along A-A′ in FIG. 11B.

FIG. 12A shows light power control to which the invention is not appliedand a spot diameter (spot shape) of laser beam when a beam diameter D is40 μm, and a left drawing is a graph showing light power of center crosssection, FIG. 12B is a schematic diagram showing light power variationwhen scanning is carried out by laser beam having the spot diameter(spot shape) shown in FIG. 12A to form a convex fine line of 21.2 μm,FIG. 12C shows a pixel exposure amount signal of laser beam, FIG. 12D isa graph showing integrating energy, of light power of laser beam ofcross section taken along the A-A′ line in FIG. 12B, and FIG. 12E is aschematic diagram showing a cross section shape of a convex fine line Ptaken along the line A-A′ in FIG. 12B.

FIG. 13A shows light power control to which the invention is not appliedand a spot diameter (spot shape) of laser beam when a beam diameter D is40 μm, and is a graph showing light power distribution of center crosssection, FIG. 13B is a schematic diagram showing light power variationwhen scanning is carried out by laser beam having the spot diameter(spot shape) shown in FIG. 13A to form a convex fine line of 21.2 μm,FIG. 13C shows a pixel exposure amount signal of laser beam, FIG. 13D isa graph showing integrating energy, of light power of laser beam ofcross section taken along the A-A′ line in FIG. 13B, and FIG. 13E is aschematic diagram showing a cross section shape of a convex fine line Ptaken along the line A-A in FIG. 13B.

FIG. 14A shows light power control to which the invention is not appliedand a pixel exposure amount signal of laser beam when a beam diameter Dis 40 μm, FIG. 14B is a graph showing integrating energy, of light powerof laser beam, and FIG. 14C schematically shows a cross section shape ofa convex fine line P.

FIG. 15A shows light power control to which the invention is applied anda pixel exposure amount signal of laser beam when a beam diameter D is40 μm, FIG. 15B is a graph showing integrating energy, of light power oflaser beam, and FIG. 15C schematically shows a cross section shape of aconvex fine line P.

FIG. 16A shows light power control to which the invention is applied anda pixel exposure amount signal of laser beam when a beam diameter D is20 μm, FIG. 16B is a graph showing integrating energy, of light power oflaser beam, and FIG. 16C schematically shows a cross section shape of aconvex fine line P.

FIG. 17A shows light power control to which the invention is applied anda pixel exposure amount signal of laser beam when a beam diameter D is20 μm, FIG. 17B is a graph showing integrating energy, of light power oflaser beam, and FIG. 17C schematically shows a cross section shape of aconvex fine line P.

FIG. 18A shows light power control to which the invention is applied anda pixel exposure amount signal of laser beam when a beam diameter D is20 μm, FIG. 18B is a graph showing integrating energy, of light power oflaser beam, and FIG. 18C schematically shows a cross section shape of aconvex fine line P.

FIG. 19A shows light power control to which the invention is not appliedand a pixel exposure amount signal of laser beam when a beam diameter Dis 40 μm, FIG. 19B is a graph showing integrating energy, of light powerof laser beam, and FIG. 19C schematically shows a cross section shape ofa convex fine line P.

FIG. 20 is an explanatory diagram schematically showing an essentialportion of an exposure head and emitted laser beam.

FIG. 21 schematically shows a cross section shape taken along ahorizontal scanning direction of a region W to be left in a convex form.

FIG. 22A is an explanatory diagram schematically showing engraving bylaser beam LA, and FIG. 22B is a graph showing light power control ofthe laser beam LA.

FIG. 23A is an explanatory diagram schematically showing engraving bylaser beam LB, and FIG. 23B is a graph showing light power control ofthe laser beam LB.

FIG. 24 is a graph showing light power control of the laser beam LA.

FIG. 25A is an explanatory diagram schematically showing engraving bylaser beam LA, and FIG. 25B is a graph showing light power control ofthe laser beam LA.

FIG. 26A is an explanatory diagram schematically showing engraving bylaser beam LB, and FIG. 26B is a graph showing light power control ofthe laser beam LB.

FIG. 27A schematically showing a cross section shape taken along ahorizontal scanning direction of a region W to be left in a convex form,FIG. 27B is a graph showing light power control of laser beam LA andlaser beam LB, and FIG. 27C is a graph showing total energy, of thelaser beam LA and laser beam LB.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. Exemplary Embodiment 1

A structure of a printing plate making apparatus 11 according to anexemplary embodiment of the present invention will be explained. Theprinting plate making apparatus 11 rotates, in a horizontal scanningdirection, a drum 50 having an outer peripheral surface to which arecording plate F (recording medium) is attached, emits a plurality oflaser beams in accordance with image data of an image to be engraved(recorded) on the recording plate F, scans an exposure head 30 in avertical scanning direction that is perpendicular to the horizontaldirection at predetermined pitch, engraves (records) a two-dimensionalimage on the recording plate at high speed, and makes a relief printingplate.

When a narrow region (fine line or meshed point) is to be left, therecording plate F is engraved shallowly (precisely engraved), and when awide region is to be left, the recording plate F is deeply engraved(roughly engraved).

FIG. 1 is a schematic diagram of a structure (perspective view) showingthe printing plate making apparatus 11. As shown in FIG. 1, the printingplate making apparatus 11 includes the drum 50 to which a recordingplate F is attached. The recording plate F is engraved by means of laserbeam and an image is recorded on the recording plate F. The drum 50 isrotated and driven in the direction of the arrow R shown in FIG. 1 sothat the recording plate F is moved in the horizontal scanningdirection. The printing plate making apparatus 11 also includes a laserrecording device 10. The laser recording device 10 includes a lightsource unit 20 as a fiber array light source which produces a pluralityof laser beams, the exposure head 30 which exposes the recording plate Fto the plurality of laser beams produced by the light source unit 20,and an exposure head moving portion 40 which moves the exposure head 30along the vertical scanning direction. A rotation direction R of thedrum 50 is the horizontal scanning direction, and a direction (detailswill be described later) in which the exposure head 30 is moved along anaxial direction (longitudinal direction) of the drum 50 shown by arrow Sis the vertical scanning direction.

The light source unit 20 includes 32 semiconductor lasers 21A and 32semiconductor lasers 21B (total 64 semiconductor lasers) comprisingbroad area semiconductor lasers to which one ends of optical fibers 22Aand 22B are respectively coupled, light source substrates 24A and 24B onwhich the semiconductor lasers 21A and 21B are disposed, adaptersubstrates 23A and 23B which are vertically mounted on one ends of thelight source substrates 24A and 24B and which are provided with aplurality of (as many as the semiconductor lasers 21A and 21B) adaptersof SC-type light connectors 25A and 25B, and LD driver substrates 27Aand 27B which are horizontally mounted on the other ends of the lightsource substrates 24A and 24B and which are provided with an LD drivercircuit 26 (see FIG. 6) for driving the semiconductor lasers 21A and 21Bin accordance with image data of an image to be engraved (recorded) onthe recording plate F.

The SC-type light connectors 25A and 25B are provided on the other endsof the optical fibers 22A and 22B, and the SC-type light connectors 25Aand 25B are connected to adapter substrates 25A and 25B. Therefore,laser beams emitted from the semiconductor lasers 21A and 21B aretransmitted to the SC-type light connectors 25A and 25B connected to theadapter substrates 23A and 23B through the optical fibers 22A and 22B.

Output terminals for driving signals of the semiconductor lasers 21A and21B in the LD driver circuit 26 provided on the LD driver substrates 27Aand 27B are respectively connected to the semiconductor lasers 21A and21B, and driving operations of the semiconductor lasers 21A and 21B areindividually controlled by the LD driver circuit 26 (see FIG. 6).

The exposure head 30 includes a fiber array portion 300 (see FIG. 2)which collectively emits laser beams emitted from the plurality ofsemiconductor lasers 21A and 21B. Laser beams emitted from thesemiconductor lasers 21A and 21B are transmitted to the fiber arrayportion 300 through a plurality of optical fibers 70A and 70B connectedto the SC-type light connectors 25A and 25B connected to the adaptersubstrates 23A and 23B.

FIG. 3 shows a light-exposing portion 280 (see FIG. 2) of the fiberarray portion 300 as viewed in the direction of the arrow A shown inFIG. 1. As shown in FIG. 3, the light-exposing portion 280 of the fiberarray portion 300 includes two pedestals 302A and 302B. V-grooves 282Aand 282B as many as (32) the semiconductor lasers 21A and 21B are formedin one surfaces of the pedestals 302A and 302B, respectively such thatthe grooves are adjacent at predetermined distances from one another. Inthe pedestals 302A and 302B, the V-grooves 282A and 282B are opposed toeach other.

Optical fiber ends 71A of the other ends of the optical fibers 70A arefitted into the V-grooves 282A of the pedestal 302A one each. Similarly,optical fiber ends 71B of the other ends of the optical fibers 70B arefitted into the V-grooves 282B of the pedestal 302B one each. Therefore,a plurality of, in this exemplary embodiment 64 (32×2) laser beamsemitted from the semiconductor lasers 21A and 21B are simultaneouslyemitted from the light-exposing portion 280 of the fiber array portion300.

That is, the fiber array portion 300 of the exemplary embodimentincludes two lines of optical fiber end groups 301A and 301B in which aplurality of (in this exemplary embodiment, total 64 (32×2)) opticalfiber ends 71A and 72B are straightly arranged in a predetermineddirection. The optical fiber end groups 301A and 301B are providedparallel in a direction intersecting with the predetermined direction.

As shown in FIGS. 1 and 3, in the laser recording device 10 of theexemplary embodiment, the predetermined direction of the fiber arrayportion 300 (exposure head 30) having the above-described structure isinclined with respect to the vertical scanning direction. As shown inFIGS. 3 and 4, the optical fiber end group 301A and the optical fiberend group 301B are arranged such that they are not overlapped each otherin the vertical scanning direction as viewing the fiber array portion300 in the horizontal scanning direction.

As shown in FIG. 1, a collimator lens 32, an opening member 33 and animaging lens 34 are arranged in this order on the exposure head 30 fromthe side of the fiber array portion 300. The opening member 33 isdisposed such that its opening is located at a far field as viewed fromthe fiber array portion 300. With this, equal light amount limitingeffect may be applied to all of laser beams emitted from the opticalfiber ends 71A and 72B of the plurality of optical fibers 70A and 70B inthe fiber array portion 300.

In this exemplary embodiment, to obtain high output laser beams,multi-mode optical fibers having relatively large core diameters areapplied to the optical fibers 22A and 22B. More specifically, in thisexemplary embodiment, the core diameter is 105 μm. The semiconductorlasers 21A and 21B having the maximum output of 8.5 w (6397-L3) areused. Core diameters of the optical fibers 70A and 70B are 105 μm.

As shown in FIG. 8, a laser beam is imaged near an exposure surface(surface) FA of the recording plate F by imaging means comprising acollimator lens 32 and an imaging lens 34 (opening member 33 is notshown in FIG. 8). In this exemplary embodiment, it is preferable that animaging position (imaging position) X is set on an exposure surface FAin terms of fine line reproducibility. A laser beam emitted from theoptical fiber end 71A (optical fiber end group 301A) is defined as alaser beam LA, and a laser beam emitted from the optical fiber end 72B(optical fiber end group 301B) is defined as a laser beam LB. When it isunnecessary to distinguish both the laser beams, it is simply describedas “laser beam”.

The optical fiber ends 71B of the end of the optical fiber end group301B is arranged next to the optical fiber end 71A of the end of theoptical fiber end group 301A (see FIG. 3 also). In FIG. 4, the number ofthe optical fiber ends 71A and 72B is lower than the actual number sothat the drawing may be understood easily.

As shown in FIG. 5, the recording plate F which is engraved by laserbeam and on which an image is to be recorded is attached to an outerperipheral surface of the drum 50 which is rotated and driven in thedirection of the arrow R. The recording plate F is attached to the outerperipheral surface of the drum 50 by a band-like chuck member 98 inwhich a rotational axial direction of the drum 50 is the longitudinaldirection. More specifically, the chuck member 98 is attached to thedrum 50 such that butted portions between the ends FT of the recordingplate F are pressed from above and with this, the recording plate F isattached to the outer peripheral surface of the drum 50. The portion ofthe chuck member 98 is non-recording region.

As shown in FIGS. 1 and 5, the exposure head moving portion 40 includesa ball screw 41 and two rails 42 (see FIG. 1) disposed such that thelongitudinal direction extends along the vertical scanning direction. Byoperating a vertical scanning motor 43 which rotates and drives the ballscrew 41, a pedestal 310 provided with the exposure head 30 may be movedin the vertical scanning direction in a state where the pedestal 310 isguided by the rails 42. By operating a horizontal scanning motor 51 (seeFIG. 6), the drum 50 may be rotated in the direction of the arrow R inFIG. 1 and with this, horizontal scanning is carried out. The exposurehead 30 is provided on the pedestal 310.

In this exemplary embodiment, exposing and scanning operations arecarried out by 64 laser beams LA and LB at a time as described above.

Next, a structure of a control system of the printing plate makingapparatus 11 (see FIG. 1) of the exemplary embodiment will be described.

As shown in FIG. 6, the control system of the printing plate makingapparatus 11 the LD driver circuit 26 which drives the semiconductorlasers 21A and 21B in accordance with image data, a horizontal scanningmotor driving circuit 81 which drives the horizontal scanning motor 51,a vertical scanning motor driving circuit 82 which drives the verticalscanning motor 43, an actuator driving circuit 299 which drives anactuator 304, and a control circuit 80 which controls the horizontalscanning motor driving circuit 81, the vertical scanning motor drivingcircuit 82 and the actuator driving circuit. Image data indicative of animage to be engraved (recorded) in the recording plate F is supplied tothe control circuit 80.

Next, a general outline of procedure for engraving (recording) on therecording plate F by the printing plate making apparatus 11 (see FIG. 1)constituted as described above will be described. FIG. 7 is a flowchartshowing a flow of processing when an image is recorded by the printingplate making apparatus 11.

As shown in FIG. 7, image data of an image to be engraved (recorded) onthe recording plate F is transferred to the control circuit 80 from animage memory (not shown) which temporarily stores the image data (step100). The control circuit 80 supplies an adjusted signal to the LDdriver circuit 26, the horizontal scanning motor driving circuit 81, thevertical scanning motor driving circuit 82, and the actuator drivingcircuit 299 based on transferred image data, resolution data indicativeof predetermined resolution of a recorded image and data indicative ofshallow engraving and deep engraving.

Next, the horizontal scanning motor driving circuit 81 controls thehorizontal scanning motor 51 such that the drum 50 rotates in thedirection of the arrow R in FIG. 1 at a rotation speed based on a signalsupplied from the control circuit 80 (step 102).

The vertical scanning motor driving circuit 82 sets a sending distanceof the exposure head 30 in the vertical scanning direction by thevertical scanning motor 43 (step 104).

Next, the LD driver circuit 26 controls the driving operations of thesemiconductor lasers 21A and 21B in accordance with image data (step106).

The laser beams LA and LB emitted from the semiconductor lasers 21A and21B are emitted from the optical fiber ends 71A and 72B of the fiberarray portion 300 through the optical fibers 22A and 22B, the SC-typelight connectors 25A and 25B and the optical fibers 70A and 70B, thelaser beams are brought into substantially parallel pencils of light bythe collimator lens 32 and then, the light amount is limited by theopening member 33, and an image is formed (focused) near the exposuresurface FA of the recording plate F on the drum 50 through the imaginglens 34.

In this case, beam spots are formed on the recording plate F inaccordance with laser beams LA and LB emitted from the semiconductorlasers 21. By these beam spots, the exposure head 30 is sent in thevertical scanning direction at the sending distance pitch which is setin the step 104 described above, and a two-dimensional image ofresolution indicated by the resolution data is engraved (formed) on therecording plate F by rotation of the drum 50 started by the step 102described above (step 108).

If the engraving (recording) operation of the two-dimensional image onthe recording plate F is completed, the horizontal scanning motordriving circuit 81 stops the rotation of the horizontal scanning motor51 (step 110) and then, this processing is completed.

Next, light power control of the laser beams LA and LB in step 108 willbe described, and operation and effect of the exemplary embodiment willbe described.

As shown in FIG. 4, if the optical fiber end group 301A, the opticalfiber end group 301B are viewed in the horizontal scanning direction, adistance between the optical fiber ends 71A and 72B, i.e., a distance(pixel pitch) between the scanning lines K is 10.58 μm (resolution 2400dpi), and in other words, one pixel is 10.58 μm.

A case where a convex fine line P in which a surface FA of the recordingplate F is left in a convex shape is formed will be described. In theconvex fine line P, the vertical scanning direction is a longitudinaldirection, and a desired width (width in the horizontal scanningdirection) is 21.2 μm.

First, a case where a spot diameter D of laser beam is defined as φ20 μmwill be described using FIGS. 9A to 11C.

FIGS. 9A and 10A are schematic diagrams showing the spot diameter (spotshape) of laser beam and graphs showing light power distribution ofcenter cross section. FIGS. 9B and 10B schematically show light powervariation when scanning is carried out by laser beam of the spotdiameter (spot shape) shown in FIGS. 9A and 10A to form convex finelines P of 21.2 μm. As the color is denser, the light power is stronger,and as the color is lighter, the light power is weaker. FIGS. 9C and 10Cshows pixel exposure amount signals of laser beams. FIGS. 9D and 10D aregraphs showing integrating energy, of light power of cross section takenalong the A-A lines in FIGS. 9B and 10B. FIGS. 9E and 10E schematicallyshow cross section shapes of the convex fine line P taken along the A-Alines in FIGS. 9B and 10B. In the drawings, G represents a width of onepixel (10.58 μm). FIGS. 11A, 11B and 11C only show diagramscorresponding to FIGS. 9C to 9E and 10C to 10E. The direction of thearrow R is the scanning direction of laser beam (horizontal scanningdirection in this exemplary embodiment).

An threshold engraving energy is an energy, of laser beam required forengraving a surface of a recording plate F, and if energy is smallerthan the threshold engraving energy, a recording plate F may not beengraved. In other words, if the energy is less than the thresholdengraving energy, even if the recording plate F is irradiated with laserbeam, the surface of the recording plate F is not engraved. Thethreshold engraving energy defers depending upon kinds (materials) ofthe recording plate F.

FIGS. 9A to 9E show a case where light power control when a pixelexposure amount signal of laser beam is OFF is carried out only on aportion corresponding to a convex fine line P of 21.2 μm width (lightpower control to which the invention is not applied). In this case, evenif the pixel exposure amount signal of laser beam is OFF, a region ofthe convex fine line P is also exposed to light. Thus, as shown in FIG.9E, the width of the upper surface P5 of the convex fine line P is thethreshold engraving energy or less, and thus, the cross section shape ofthe convex fine line P become substantially trapezoidal shape. The widthof the upper surface P5 of the convex fine line P is less than desired21.2 μm.

FIGS. 10A to 10E show a case where light power control when a pixelexposure amount signal of laser beam is OFF is carried out also by theeach pixel (total two pixels) of upstream and downstream of the convexfine line P of 21.2 μm width in the scanning direction. In this case,the convex fine line P portion is not completely exposed to light, thewidth of the upper surface P5 of the convex fine line P may be closer to21.2 μm which is a desired value (21.2 μm width is secured orsubstantially secured). The width of the upper surface P5 of the convexfine line P is a portion of the threshold engraving energy or less andthus, the side is wider by α1 in the drawing to be precisely. A bottomside of the trapezoidal shape shown in FIG. 10E is about 20 μm.

In the case of FIGS. 10A to 10E, although the width of the upper surfaceP5 of the convex fine line P may be close to about desired 20 μm, theinclination angles of the sidewalls P1 and P2 upstream and downstream ofthe convex fine line P in the scanning direction are gentle. The angleof the edge portion E constituted by the upper surface P5 and thesidewalls P1 and P2 falls (more than 90°). However, in order to print afile line after printing precisely, it is necessary to erect the edgeportion E (it is necessary to bring the angle close to 90°). That is, itis necessary to bring the inclination angles of the sidewalls P1 and P2close to 90° (vertical).

Hence, in the printing plate making apparatus 11 of the exemplaryembodiment, the invention is applied, the light power by outer one pixelin which laser beam is OFF is increased, thereby bringing theinclination angles of the sidewalls P1 and P2 close to 90° (vertical).That is, the edge portion E is erected (closer to 90°). With this, thecross section shape of the convex fine line P is brought closer to arectangular shape.

Since the width of the upper surface P5 of the convex fine line P is aportion where the energy is the threshold engraving energy or less andthus, to be precise, the width is wider by α2 in the drawing, howeversince the inclination angles of the sidewalls P1 and P2 are broughtcloser to vertical, this is extremely slight and no problem occurs. Theincreasing width for increasing the light power of laser beam may beincreased or width at which the pixel exposure amount signal is turnedOFF may be slightly narrowed to narrow by α2 (to bring the width closerto desired 21.2 μm).

In the printing plate making apparatus 11 of this exemplary embodiment,the light power is turned OFF in one pixel upstream and downstream inthe scanning direction in region adjacent to the convex fine line P, thelight power of one pixel (vicinity region) in vicinity of outer sidewhere the laser beam is turned OFF is increased, whereby bringing theinclination angles of the sidewalls P1 and P2 closer to vertical (edgeportion E is erected (closer to 90°)).

Even if the beam diameter D is as large as 20 μm (even if beam diameterD is more than one pixel), if the light power control of the inventionis applied, the width of the upper surface P5 of the convex fine line Pmay be brought closer to the desired width (21.2 μm in this exemplaryembodiment), and the cross section shape of the convex fine line P maybe brought closer to the rectangular shape. That is, the convex fineline P may precisely be engraved. Thus, the reproducibility of fine linein a printing medium printed by a recording plate F after the plate ismade may be enhanced.

As shown in FIGS. 18A to 18C, the pixel exposure amount signal of thelaser beam may not be turned OFF (light power is 0(zero)) by one pixel(total two pixels) upstream and downstream in the scanning direction ofthe convex fine line P having about 20 μm width, and the light powercontrol may be performed such that exposure is carried out at thresholdengraving energy or less.

Next, a case where the spot diameter D of laser beam is φ40 μm will bedescribed using FIGS. 12A to 15C.

In FIGS. 12A to 13E, like the case where the spot diameter D is φ20 μm,right drawings of FIGS. 12A and 13A show spot diameters (spot shapes) oflaser beams, and left drawings are graphs showing light powerdistributions of center cross sections. FIGS. 12B and 13B schematicallyshow light power variation when scanning is carried out by laser beam ofthe spot diameter (spot shape) shown in FIGS. 12A and 13A to form convexfine lines P of 20 μm. As the color is denser, the light power isstronger, and as the color is lighter, the light power is weaker. FIGS.12C and 13C shows pixel exposure amount signals of laser beams. FIG. 12Dis a graph showing integrating energy, of light power of cross sectiontaken along the A-A line in FIG. 12B. FIG. 12E schematically shows across section shape taken along the A-A line in FIG. 12B. In thedrawings, G represents a width of one pixel (10.58 μm). FIGS. 14A to14C, and 15A to 15C only show diagrams corresponding to FIGS. 12C to 12Eand 13C to 13E. The direction of the arrow R in the drawing is thescanning direction of laser beam (horizontal scanning direction in thisexemplary embodiment).

FIGS. 12A to 12E show a case where light power control in which anexposure signal of laser beam only in a portion corresponding to theconvex fine line P of 21.2 μm width is turned OFF is carried out (lightpower control to which the invention is not applied). In this case, evenif the pixel exposure amount signal of laser beam is turned OFF, theconvex fine line P is also exposed to light. Further, since the spotdiameter D is as large as φ40 μm, as shown in FIG. 12D, laser beams areoverlapped on the convex fine line P and the integrating energy isincreased. Therefore, the convex fine line P is not formed as shown inFIG. 12E.

FIGS. 13A to 13E show a case where light power control in which a pixelexposure amount signal of laser beam is turned OFF also in one pixel(total two pixels) upstream and downstream of the convex fine line P of21.2 μm width in the scanning direction is carried out (light powercontrol to which the invention is not applied). In this case also, sincethe spot diameter D is as large as φ40 μm, the convex fine line P isalso exposed to light. Thus, as shown in FIG. 13E, the width of theupper surface P5 of the convex fine line P becomes a portion where theenergy is the threshold engraving energy or less, the cross sectionshape becomes substantially trapezoidal shape. Thus, the width of theupper surface P5 of the convex fine line P is less than the desired 20μm.

FIGS. 14A to 14C show a case where light power control in which a pixelexposure amount signal of laser beam of two pixels (total four pixels)upstream and downstream of the convex fine line P of 21.2 μm width isturned OFF is carried out (light power control to which the invention isnot applied). In this case, since the portion of the convex fine line Pis not substantially completely exposed to light, the width of the uppersurface P5 of the convex fine line P may be closer to the desired valueof 21.2 μm.

In this case, although the width of the upper surface P5 of the convexfine line P may be brought closer to the desired 21.2 μm, theinclination angles of the sidewalls P1 and P2 upstream and downstream ofthe convex fine line P are gentle as shown in FIG. 14C. That is, theangle of the edge portion E constituted by the upper surface P5 and thesidewalls P1 and P2 fall (the angle is more than 90°). To enhance theprecision of fine line after printing, it is necessary to erect the edgeportion E (it is necessary to bring the angle closer to 90°). That is,it is necessary to bring the inclination angles of the sidewalls P1 andP2 closer to vertical (90°).

Hence, like the case where the beam diameter D is 20 μm as describedabove, the invention is applied, as shown in FIGS. 15A to 15C, the lightpower of one pixel on the outer side where the laser beam is turned OFFis increased, the inclinations of the sidewalls P1 and P2 are broughtcloser to vertical ((closer to 90°) by more erecting the edge portionE), and the cross section shape of the convex fine line P may be broughtcloser to the rectangular shape.

Even if the beam diameter D is as large as 40 μm (even if the beamdiameter D is more than one pixel and more than the width of the convexfine line P), if the invention is applied, the upper surface P5 of theconvex fine line P may be brought closer to the desired 20 μm, and tobring the cross section shape of the convex fine line P close to therectangular shape. That is, even if the beam diameter D is as large as40 μm, the convex fine line P may be engraved precisely. Thus, thereproducibility of fine line on a printing medium printed by therecording plate F after the plate is made may be enhanced.

As shown in FIGS. 19A to 19C, the pixel exposure amount signal of laserbeam in two pixels (total four pixels) upstream and downstream of theconvex fine line P of about 20 μm width may be not turned OFF, and thelight power control for exposing to threshold engraving energy or lessmay be carried out. In this case also, the power light amount of onepixel on the outer side where the laser beam is the threshold engravingenergy or less is increased, the inclinations of the sidewalls P1 and P2are brought closer to vertical ((closer to 90°) by more erecting theedge portion E), the cross section shape of the convex fine line P isbrought closer to the rectangular shape.

The laser beam diameter D may be the same as or different from those ofthe laser beam LA and laser beam LB (see FIG. 8). For example, a beamdiameter D of laser beam LA for shallow engraving may be 20 μm and abeam diameter D of laser beam LB for deep engraving may be 40 μm.

Next, light power control which is carried out in such a manner thatwhen power light amount of one pixel on the outer side where laser beamis turned OFF (or the threshold engraving energy or less) is increased,the pulse exposure is carried out, thereby bringing the inclinations ofthe sidewalls P1 and P2 to the vertical ((closer to 90°) by moreerecting the edge portion E). This light power control will bedescribed. In other words, light power control for bringing the crosssection shape of the convex fine line P closer to the rectangular shapewill be described.

In this description, the beam diameter D is about 20 μm, but even if thebeam diameter D is 40 μm, nothing is changed.

FIGS. 16A to 16C show a case where pulse exposure is carried out withpulse width of 0.5 pixels. As may be found from FIGS. 16A to 16C, theinclinations of the sidewalls P1 and P2 may be brought closer tovertical. At that time, it is preferable that the maximum value of lightpower is increased such that the integrating energy becomessubstantially equal to that shown in FIGS. 11A to 11C.

FIGS. 17A and 17C show a case where pulse exposure is carried out withpulse width of 0.25 pixels. As may be found in FIGS. 17A to 17C, if thepulse width is further narrowed, the inclinations of the sidewalls P1and P2 may be brought closer to vertical. At that time, it is preferablefurther increase the maximum value of light power so that theintegrating energy becomes substantially equal to that shown in FIGS.11A to 11C (16A to 16C).

Next, other operation and effect of the exemplary embodiment will bedescribed.

In this exemplary embodiment, the laser exposure system which emitslaser beam is the fiber array exposure system which emits laser beamfrom the light source unit 20 (fiber array light source) and thenfocuses the laser beam by the imaging lens 34. This laser exposuresystem may be produced inexpensively as compared with a laser exposuresystem using fiber laser or CO2 laser light source.

For example, in the exemplary embodiment, the light power is controlledon both upstream and downstream in the horizontal scanning direction,however the light power may be controlled only one of upstream anddownstream.

Further, the light power control of the invention may be applied to atleast one of upstream and downstream in the vertical scanning directioninstead of upstream and downstream in the horizontal scanning direction.That is, the width of the upper surface P5 in the cross section takenalong the B-B′ line shown in FIG. 9 may be brought closer to the desired21.2 μm, and the cross section may be brought closer to the rectangularshape (sidewalls P3 and P4 are also brought close to vertical).

The threshold engraving energy is light energy, of light beam requiredfor engraving a surface of a recording medium. If the energy is morethan the threshold engraving energy, a recording medium may not beengraved. The threshold engraving energy is a technique not disclosed inthe prior art, and if this is taken into consideration, the plate may beengraved more finely.

2. Exemplary Embodiment 2

A printing plate making apparatus of an exemplary embodiment 2 has thesame structure as that of the exemplary embodiment 1 as a whole.

However, as shown in FIG. 20, an image of laser beam is formed near anexposure surface (surface) FA of the recording plate F constituted by acollimator lens 32 and an imaging lens 34 (the opening member 33 is notshown in FIG. 20), and a clear plate-like imaging position shift member350 is disposed in front of an optical fiber end group 301A (opticalfiber end 71A) as imaging position changing means. With this, an imagingposition of laser beam LA emitted from the optical fiber end group 301A(optical fiber end 71A) is shifted toward the exposure surface FA. Theimaging position of the laser beam LA is defined as a first imagingposition X1, and the imaging position of the laser beam LB is defined asa second imaging position X2.

Next, control procedure of light power of laser beams LA and LB in step108 will be described.

As shown in FIG. 4, if the optical fiber end group 301A and the opticalfiber end group 301B are viewed in the horizontal scanning direction, adistance between the optical fiber ends 71A and 72B, i.e., a distancebetween scanning lines K (pixel pitch) is defined as 10.58 μm(resolution 2400 dpi). In other words, one pixel is defined as 10.58 μm.

The printing plate making apparatus 11 of the exemplary embodiment 2shallowly engraves the recording plate F when engraving a narrow region(precise engraving of fine line or meshed point) and deeply engraves therecording plate F when engraving a wide region.

More specifically, when shallowly engraving, the output (power) of laserbeam is reduced, an image is scanned by laser beam LA emitted from theoptical fiber end 71A of mainly the optical fibers 70A (optical fiberend group 301A) to engrave a printing plate.

When deeply engraving, the output (power) of laser beam is increased, aprinting plate is engraved to a first depth L1 by laser beam LA emittedfrom the optical fiber end 71A of the optical fibers 70A (optical fiberend group 301A) and then, the same scanning lines K (see FIG. 6) areengraved to a second depth L2 by laser beam LB emitted from the opticalfiber ends 71B of the optical fiber 70B (optical fiber end group 301B).In this exemplary embodiment, the first depth L1 is 250 μm and thesecond depth L2 is 500 μm.

At the time of this deep engraving, a case where a region (left inconvex shape) is formed in the recording plate F as shown in FIG. 21will be described. A cross section of the region W extending along thehorizontal scanning direction has such a shape that a convex fine line Phaving a rectangular cross section is formed on an upper portion (on anupper bottom) of a foundation D having a substantially trapezoidal crosssection. An upstream end PA located upstream of the convex fine line Pin the scanning direction constituting an upper portion of the region Wwhere the recording plate F is left in a convex shape is defined as anupstream reference position, and a downstream end PB located downstreamin the scanning direction is defined as an upstream reference position.The convex fine line P has a vertical scanning direction in thelongitudinal direction.

In this exemplary embodiment, the light power P1 of the laser beam LAand the light power P2 of the laser beam LB are the same. However, theinvention is not limited to this (the light power P1 of the laser beamLA and the light power P2 of the laser beam LB may be different fromeach other).

Here, the light power control for forming the region W shown in FIG. 21will be described using FIGS. 22A to 23B. FIG. 22A is an explanatorydiagram schematically showing engraving by laser beam LA, and FIG. 22Bis a graph showing the light power control of laser beam LA. Similarly,FIG. 23A is an explanatory diagram schematically showing engraving bylaser beam LB, and FIG. 23B is a graph showing the light power controlof laser beam LB.

As shown in FIGS. 22A and 22B, the recording plate F is scanned by thelaser beam LA in a predetermined pixel pitch (10.58 μm pitch in theexemplary embodiment) and engraved at the first depth L1. At that time,light power of laser beam LA is reduced from P1 linearly orsubstantially linearly from a first point Q1 or the vicinity thereofalong a line segment connecting the first point Q1 in a first depth L1separated from an upstream reference position (PA) by m pixels upstreamin the scanning direction and a second point Q2 separated from theupstream reference position (PA) on a surface FA of the recording plateF by n pixels downstream in the scanning direction, and the energy isreduced to the threshold engraving energy or less at the upstreamreference position (PA) or the vicinity thereof (PA) (in this exemplaryembodiment, the exposure light is turned OFF (light power is set to 0)).That is, the light power of laser beam LA starts lowering from the firstpoint Q1 or the vicinity thereof and the energy is set to thresholdengraving energy or less at the upstream reference position (PA) or thevicinity thereof (PA).

The threshold engraving energy is energy, of laser beam required forengraving a surface of a recording plate F, and if the energy is morethan the threshold engraving energy, the recording plate F may not beengraved. In other words, if the energy is less than the thresholdengraving energy or less, even if the recording plate F is irradiatedwith laser beam, the surface of the recording plate F is not engraved.The threshold engraving energy defers depending upon kinds (materials)of the recording plate F.

A width of the convex fine line P in the scanning direction is scannedat threshold engraving energy or less (in this exemplary embodiment, theexposure is turned OFF) and then, light power of laser beam LA is set soas to be equal or higher than the threshold engraving energy, from thedownstream reference position or the vicinity thereof (in this exemplaryembodiment, the exposure is turned ON), the light power is increased tolinearly or substantially linearly and this point is defined as a fifthpoint Q5 or near P. At that time, the light power is increased linearlyor substantially linearly along a line segment connecting a fifth pointQ5 in the first depth L1 separated from the downstream referenceposition (PB) by m pixels downstream in the scanning direction and asixth point Q6 separated from the downstream reference position in thesurface FA of the recording plate F by n pixels upstream in the scanningdirection.

Next, as shown in FIGS. 23A and 23B, the recording plate F is scanned ata predetermined pixel by laser beam LB and the plate is engraved at thesecond depth L2. At that time, the light power of laser beam LB isreduced from P2 linearly or substantially linearly from a third point Q3or the vicinity thereof along a line segment connecting the first pointQ1 and a third point Q3 in the second depth L2 separated from theupstream reference position (PA) by (2m+n) pixels upstream in thescanning direction, and the energy is set to the threshold engravingenergy or less at the first point Q1 or the vicinity thereof (in thisexemplary embodiment, the exposure is turned OFF (light power is set to0)). That is, light power of laser beam LB starts lowering from thethird point Q3 or the vicinity thereof, and the energy is set tothreshold engraving energy or less at the first point Q1 or the vicinitythereof.

The width of the convex fine line P in the scanning direction is scannedat the threshold engraving energy or less (in this exemplary embodiment,the exposure is turned OFF) and then, the light power of the laser beamLB is set so as to be equal or higher than the threshold engravingenergy, from the fifth point Q5 or the vicinity thereof (in thisexemplary embodiment, exposure is turned ON), the light power isincreased linearly or substantially linearly, and the light power is setto P2 at a seventh point Q7 or the vicinity thereof. At that time, thelight power is increased linearly or substantially linearly along a linesegment connecting the fifth point Q5 and the seventh point Q7separating from the downstream reference position (PB) in the seconddepth L2 downstream in the scanning direction by (2m+n) pixels.

By performing such light power control, even when the recording plate Fis scanned twice and is engraved, the region W to be left in a convexshape may be brought close into such a shape that a convex fine line Phaving a substantially rectangular cross section is formed on top of afoundation D having a substantially trapezoidal cross section. Anupstream inclined surface DA of the foundation D having a substantiallytrapezoidal cross section in the scanning direction becomes asubstantially straight line. Similarly, a downstream inclined surface DBof the foundation D having a substantially trapezoidal cross section inthe scanning direction becomes a substantially straight line. In otherwords, an inclined surface of a foundation engraved by the laser beam LBis substantially straightly connected to an inclined surface of afoundation engraved by the laser beam LA.

When the printing is carried out using a recording plate F (printingplate) after the plate is made, a case where a printing density isvaried depending upon a pressing force against a printing medium, and acase where a fine line or highlight point is not printed clearly areprevented or suppressed, and clear printing may be carried out.

In this exemplary embodiment, since P1=P2, the first point Q1 and theseventh point Q7 are separated from the upstream reference position (PA)or the downstream reference position (PB) by (2m+n) pixels. However,when P1 and P2 are different from each other, the first point Q1 and theseventh point Q7 may be located at positions separated from the upstreamreference position or downstream reference position by (2m+n)×(P2/P1)pixel.

Next, “n” and “m” will be described.

It is preferable that n is an integer from 1 to 3. That is, if n is aninteger from 1 to 3, the convex fine line P having the substantiallyrectangular cross section is set to appropriate height.

It is preferable that m is an integer from 5 to 30. That is if m is theinteger from 5 to 30, the foundation D having a substantiallytrapezoidal cross section is set to appropriate width.

The “convex fine line P has appropriate height” and the “foundation Dhaving a substantially trapezoidal cross section has appropriate width”mean that when printing is carried out using a recording plate F(printing plate) after the plate is made, the “height” and “width” areset to such values that a case where a printing density is varieddepending upon a pressing force against a printing medium, and a casewhere a fine line or highlight point is not printed clearly areprevented or suppressed, and clear printing may be carried out.

Next, control of light power of laser beam LA for bringing a width ofthe convex fine line P in the scanning direction close to apredetermined width, and bringing a rectangular cross section to arectangular shape will be described using FIG. 12. In the drawings, Grepresents one pixel (10.58 μm).

Even if a pixel exposure amount signal of laser beam LA is turned OFF,an upper surface of the convex fine line P is exposed to light. Thus,the width of the upper surface of the convex fine line P does not reacha desired width in some cases.

Hence, light power control in which a pixel exposure amount signal oflaser beam LA is turned OFF is carried out also for one pixel of theconvex fine line P upstream in the scanning direction. The engraving iscarried out while increasing the light power than a line segmentconnecting the first point Q1 and the second point Q2 by one pixel onthe outer side upstream in the scanning direction in which laser beam LAis turned OFF.

Similarly, light power control in which the pixel exposure amount signalof laser beam LA is turned OFF is carried out also for one pixel of theconvex fine line P downstream in the scanning direction. The engravingis carried out while increasing the light power than a line segmentconnecting the fifth point Q5 and the sixth point Q6 by one pixel on theouter side downstream in the scanning direction in which laser beam LAis turned OFF.

By performing such light power control, the width of the upper surfaceP5 of the convex fine line P may be brought closer to the desired widthand the edge portion (PA, PB) further erect (brought closer to 90°).That is, the cross section shape of the convex fine line P becomescloser to the rectangular shape (the convex fine line P is preciselyengraved). Thus, reproducibility of fine line on a printing mediumprinted by a recording plate F after the plate is made is enhanced.

Although the scanning is carried out using laser beam LA and then thescanning is carried out using laser beam LB in this control method, theinvention is not limited to this. Even when the scanning is carried outusing laser beam LB and then the scanning is carried out using laserbeam LA, if the same power control is performed, the shape of the regionW to be left in a convex shape may be brought close into such a shapethat a convex fine line P having a substantially rectangular crosssection is formed on top of a foundation D having a substantiallytrapezoidal cross section.

Next, the fact that the same engraved shape may be obtained irrespectiveof which one of laser beam LA and laser beam LB is scanned first, i.e.,the fact that the shape of the region W to be left in a convex shape maybe brought close into such a shape that a convex fine line P having asubstantially rectangular cross section is formed on top of a foundationD having a substantially trapezoidal cross section irrespective of whichone of laser beam LA and laser beam LB is scanned first will bedescribed.

A depth which may be engraved by laser beam LA is defined as d1 as shownin FIG. 25A, and a depth which may be engraved by laser beam LB isdefined as d2 as shown in FIG. 26A. Here, the depth of d1+d2 is equal tothe second depth L2.

As shown in FIG. 25B, when scanning operation is carried out using laserbeam LA to engrave, the light power of the laser beam LA is reduced fromP1 linearly or substantially linearly from a first point or the vicinitythereof along a line segment connecting the first point separated fromthe upstream reference position upstream in the scanning direction by mpixels and a second point separated from the upstream reference positionon the surface FA of the recording plate F downstream in the scanningdirection, and the energy is set to the threshold engraving energy orless at the upstream reference position or the vicinity thereof. Thatis, the light power of laser beam LA starts lowering from the firstpoint or the vicinity thereof, and the energy is set to the thresholdengraving energy or less at the upstream reference position or thevicinity thereof.

The scanning is carried out while the width of the convex fine line P inthe scanning direction is set to the threshold engraving energy or lessand then, the light power of the laser beam LA is increased linearly orsubstantially linearly to the threshold engraving energy or higher fromthe downstream reference position or the vicinity thereof, and the pointis set to P1 at the fifth point or the vicinity thereof. At that time,the light power is increased linearly or substantially linearly along aline segment connecting the fifth point separated away from thedownstream reference position downstream in the scanning direction by mpixels and the sixth point separated away from the downstream referenceposition in the surface FA of the recording plate F upstream in thescanning direction by n pixels.

As shown in FIG. 26B, when scanning is carried out by laser beam LB andengraving the plate, the light power of the laser beam LB is reducedfrom P2 linearly or substantially linearly from the third point or thevicinity thereof along a line segment connecting the third pointseparated away from the upstream reference position upstream in thescanning direction in (2n+m) pixels and the first point, and the energyis set to the threshold engraving energy or less at the first point orthe vicinity thereof. That is, the light power of the laser beam LBstarts lowering at the third point or the vicinity thereof, and theenergy, becomes the threshold engraving energy or lower at the firstpoint or the vicinity thereof.

The width of the convex fine line P in the scanning direction is set tothe threshold engraving energy or less and the scanning is carried outand then, the light power of the laser beam LB is increased to thethreshold engraving energy or higher from the fifth point or thevicinity thereof, the light power is increased linearly or substantiallylinearly, and the point is set to P2 at the seventh point or thevicinity thereof. The light power is increased linearly or substantiallylinearly along a line segment connecting the fifth point and the seventhpoint separated away from the downstream reference position downstreamin the scanning direction by (2m+n) pixels.

Here, if the scanning is carried out by the laser beam LB after thescanning is carried out by the laser beam LA, the light power control isthe same as that described heretofore. Even when the scanning is carriedout by the laser beam LA after the scanning is carried out by the laserbeam LB, as shown in FIG. 27C, since the total exposure energy, of thelaser beam LA and the laser beam LB is the same, substantially the sameengraved shape may be obtained. That is, irrespective of which one ofthe laser beam LA and laser beam LB is scanned and exposed first, sincethe total exposure energy is the same, the shape of the region W to beleft in a convex shape may be brought close into such a shape that aconvex fine line P having a substantially rectangular cross section isformed on top of a foundation D having a substantially trapezoidal crosssection. FIG. 27A schematically shows the cross section shape extendingalong the horizontal scanning direction of the region W to be left tothe convex shape. FIG. 27B is a graph showing both FIGS. 25B and 26B.FIG. 27C is a graph showing the total energy, of the laser beam LA andthe laser beam LB.

In the above description, since P1=P2, the first point and the seventhpoint are separated from the upstream reference position or thedownstream reference position by (2m+n) pixels. However, when P1 and P2are different from each other, the first point Q1 or the seventh pointQ7 may be located at a position separated from the upstream referenceposition or downstream reference position by (2m+n)×(P2/P1) pixels.

As described above, the threshold engraving energy is light energy, oflight beam required to engrave a surface of a recording medium, and ifthe energy is smaller than the threshold engraving energy, a recordingmedium may not be engraved. The threshold engraving energy is atechnique that is not disclosed in the prior art, and if this energy istaken into consideration, the plate may be engraved more finely.

The invention is not limited to the exemplary embodiment.

Although the light power is controlled upstream and downstream in thehorizontal scanning direction in the exemplary embodiment, the lightpower may be controlled only one of upstream and downstream.

The light power control of the invention may be applied to at least oneof upstream and downstream in the vertical scanning direction instead ofupstream and downstream in the scanning direction (horizontal scanningdirection).

What is claimed is:
 1. A printing plate making apparatus configured toscan a recording medium by a light beam at a predetermined pixel pitch,thereby engraving a surface of the recording medium to make a printingplate, wherein: the light beam includes a first light beam and a secondlight beam, a light power of the first light beam is P1, a light powerof the second light beam is P2, and depths engraved by the respectivelight powers are d1 and d2; the printing plate making apparatus isconfigured such that, after scanning the recording medium with one ofthe first and second light beams at a predetermined pixel pitch toengrave the recording medium to a first depth d1 or d2, a scanning linescanned by the one light beam is scanned by the other of the first andsecond light beams and the recording medium is engraved to a seconddepth d1+d2 which is deeper than the first depth; an upstream end of aconvex portion forming an upper portion of a region where the recordingmedium is to be left in a convex shape is defined as an upstreamreference position; the printing plate making apparatus is configured tocontrol light power of the first light beam such that, when therecording medium is scanned at a predetermined pixel pitch with thefirst light beam, from a first point which is separated from theupstream reference position by m pixels in the scanning direction, orthe vicinity thereof, to a second point on the surface of the recordingmedium separated from the upstream reference position by n pixelsdownstream in the scanning direction, a light power of the first lightbeam is reduced linearly or substantially linearly from P1 such that atthe upstream reference position or the vicinity thereof the light powerof the first light beam is equal to or less than a threshold engravingenergy; and when the recording medium is scanned by the second lightbeam at a predetermined pixel pitch, from a third point or the vicinitythereof, the third point being separated from the upstream referenceposition by (2m+n)×(P2/P1) pixels in the scanning direction, theprinting plate making apparatus is configured to reduce the light powerof the second light beam linearly or substantially linearly from P2 suchthat it becomes the threshold engraving energy or less at the firstpoint or the vicinity thereof.
 2. The printing plate making apparatusaccording to claim 1, wherein: when engraving all or part of an adjacentregion which is adjacent upstream in the scanning direction to a convexportion forming an upper portion of a region where a surface of therecording medium is to be left in a convex shape, the printing platemaking apparatus is configured to reduce a light power of the firstlight beam so as to be equal to or less than the threshold engravingenergy, at the upper surface of the convex portion, and in a vicinityregion which is in the vicinity of an outer side of an upstream side ofthe adjacent region in the scanning direction, the printing plate makingapparatus is configured to set the light power of the first light beamhigher than the light power of the first light beam when engraving alonga line segment connecting the first point and the second point.
 3. Theprinting plate making apparatus according to claim 2, wherein n is aninteger from 1 to
 3. 4. The printing plate making apparatus according toclaim 2, wherein m is an integer from 5 to
 30. 5. The printing platemaking apparatus according to claim 1, wherein n is an integer from 1 to3.
 6. The printing plate making apparatus of claim 5, further configuredto: scan the recording medium by a light beam in a horizontal scanningdirection and a vertical scanning direction that is perpendicular to thehorizontal direction, and control light power of the light beam when therecording medium is scanned at one or both of the horizontal scanningdirection and vertical scanning direction.
 7. The printing plate makingapparatus according to claim 1, wherein m is an integer from 5 to
 30. 8.The printing plate making apparatus of claim 7, further configured to:scan the recording medium by a light beam in a horizontal scanningdirection and a vertical scanning direction that is perpendicular to thehorizontal direction, and control light power of the light beam when therecording medium is scanned at one or both of the horizontal scanningdirection and vertical scanning direction.
 9. The printing plate makingapparatus of claim 1, further configured to: scan the recording mediumby a light beam in a horizontal scanning direction and a verticalscanning direction that is perpendicular to the horizontal direction,and control light power of the light beam when the recording medium isscanned at one or both of the horizontal scanning direction and verticalscanning direction.
 10. A printing plate making apparatus configured toscan a recording medium by a light beam at a predetermined pixel pitch,thereby engraving a surface of the recording medium to make a printingplate, wherein: the light beam includes a first light beam and a secondlight beam, a light power of the first light beam is P1, a light powerof the second light beam is P2, and depths engraved by the respectivelight powers are d1 and d2; the printing plate making apparatus isconfigured such that, after scanning the recording medium with one ofthe first and second light beams at a predetermined pixel pitch toengrave the recording medium to a first depth d1 or d2, a scanning linescanned by the one light beam is scanned by the other of the first andsecond light beams and the recording medium is engraved to a seconddepth d1+d2 which is deeper than the first depth; a downstream end of aconvex portion forming an upper portion of a region where the recordingmedium is to be left in a convex shape downstream in the scanningdirection is defined as a downstream reference position; the printingplate making apparatus is configured to control light power of the lightbeam such that, when the recording medium is scanned at a predeterminedpixel pitch with the first light beam, the light power of the firstlight beam is set to be equal to or greater than the threshold engravingenergy at the downstream reference position or the vicinity thereof;from a fifth point separated from the downstream reference positiondownstream in the scanning direction by m pixels to a sixth point on asurface of the recording medium separated from the downstream referenceposition in the scanning direction by n pixels, the printing platemaking apparatus is configured to increase light power of the firstlight beam linearly or substantially linearly, and set the power of thefirst light beam to P1 at the fifth point or the vicinity thereof; andthe printing plate making apparatus is configured to control light powerof the second light beam such that, when the recording medium is scannedat a predetermined pixel pitch by the second light beam, a light powerof the second light beam is equal to or greater than the thresholdengraving energy at the fifth point or the vicinity thereof, and towardsa seventh point separated from the fifth point and the downstreamreference position downstream in the scanning direction by(2m+n)×(P2/P1) pixels, the light power is increased linearly orsubstantially linearly and set to P2 at the seventh point or thevicinity thereof.
 11. The printing plate making apparatus of claim 10,further configured to control light power of the first light beam suchthat: a light power of the first light beam, which engraves all or partof an adjacent region which is adjacent to a convex portion downstreamin the scanning direction which forms an upper portion of a region wherea surface of the recording medium is to be left in a convex shape, isreduced to be equal to or less than the value of the threshold engravingenergy at the upper surface of the convex portion, and at the vicinityregion which is in the vicinity of an outer side of an upstream side ofthe adjacent region in the scanning direction, the light power of thefirst light beam is set higher than the light power of the first lightbeam when engraving along a line segment connecting the fifth point andthe sixth point.
 12. The printing plate making apparatus according toclaim 11, wherein n is an integer from 1 to
 3. 13. The printing platemaking apparatus according to claim 11, wherein m is an integer from 5to
 30. 14. The printing plate making apparatus according to claim 10,wherein n is an integer from 1 to
 3. 15. The printing plate makingapparatus according to claim 10, wherein m is an integer from 5 to 30.16. A printing plate making method for engraving a surface of arecording medium to make a printing plate, the method comprisingscanning a recording medium with a light beam at a predetermined pixelpitch, wherein a light beam includes a first light beam and a secondlight beam, a light power of the first light beam is P1, a light powerof the second light beam is P2, and depths engraved by the respectivelight powers are d1 and d2; after the recording medium is scanned by oneof the first and second light beams at a predetermined pixel pitch tothe first depth d1 or d2, a scanning line scanned by the one light beamis scanned by the other of the first and second light beams, and therecording medium is engraved to a second depth d1+d2 which is deeperthan the first depth; an upstream end of a convex portion forming anupper portion of a region where the recording medium is to be left in aconvex shape upstream in the scanning direction is defined as anupstream reference position; light power control of the first light beamis carried out such that, when the recording medium is scanned at apredetermined pixel pitch with the first light beam, from a first pointwhich is separated from the upstream reference position by m pixels inthe scanning direction, or the vicinity thereof, to a second point onthe surface of the recording medium separated from the upstreamreference position by n pixels downstream in the scanning direction, alight power of the first light beam is reduced linearly or substantiallylinearly from P1 so that at the upstream reference position or thevicinity thereof the light power of the first light beam is equal to orless than a threshold engraving energy; and when the recording medium isscanned by the second light beam at a predetermined pixel pitch, from athird point or the vicinity thereof, the third point being separatedfrom the upstream reference position by (2m+n)×(P2/P1) pixels in thescanning direction, the light power of the second light beam is reducedlinearly or substantially linearly from P2 such that it becomes thethreshold engraving energy or less at the first point or the vicinitythereof.
 17. The printing plate making apparatus according to claim 16,wherein when engraving all or part of an adjacent region which isadjacent upstream in the scanning direction to a convex portion formingan upper portion of a region where a surface of the recording medium isto be left in a convex shape, a light power of the first light beam isreduced so as to be equal to or less than the threshold engravingenergy, at the upper surface of the convex portion, and in a vicinityregion which is in the vicinity of an outer side of an upstream side ofthe adjacent region in the scanning direction, the light power of thefirst light beam is set higher than the light power of the first lightbeam when engraving along a line segment connecting the first point andthe second point.
 18. A printing plate making method for engraving asurface of a recording medium to make a printing plate, the methodcomprising scanning a recording medium with a light beam at apredetermined pixel pitch, wherein a light beam includes a first lightbeam and a second light beam, a light power of the first light beam isP1, a light power of the second light beam is P2, and depths engraved bythe respective light powers are d1 and d2; after the recording medium isscanned by one of the first and second light beams at a predeterminedpixel pitch to engrave to the first depth d1 or d2, a scanning linescanned by the one light beam is scanned by the other of the first andsecond light beams, and the recording medium is engraved to a seconddepth d1+d2 which is deeper than the first depth; an upstream end of aconvex portion forming an upper portion of a region where the recordingmedium is to be left in a convex shape upstream in the scanningdirection is defined as an upstream reference position; when therecording medium is scanned at a predetermined pixel pitch by the firstlight beam, a light power of the first light beam is set to a thresholdengraving energy or higher from the downstream reference position or thevicinity thereof, toward a fifth point separated from the downstreamreference position downstream in the scanning direction by m pixels andtoward a sixth point on a surface of the recording medium separated by npixels from the downstream reference position in the scanning direction,the light power is increased linearly or substantially linearly so thatthe light power is P1 at the fifth point or the vicinity thereof, whenthe recording medium is scanned by the second light beam in apredetermined pixel pitch, a light power of the second light beam is setto the threshold engraving energy or higher from the fifth point or thevicinity thereof, and then, the light power is increased linearly orsubstantially linearly along a line segment connecting the fifth pointand a seventh point separated away from the downstream referenceposition downstream in the scanning direction by (2m+n)×(P2/P1) pixels,and the light power of the second light beam is set to P2 at the seventhpoint or the vicinity thereof.
 19. The printing plate making method ofclaim 18, wherein when engraving all or part of an adjacent region whichis adjacent to a convex portion downstream in the scanning directionforming an upper portion of a region where a surface of the recordingmedium is to be left in a convex shape, a light power of the first lightbeam is reduced so as to be equal to or less than the thresholdengraving energy, at the upper surface of the convex portion, and at thevicinity region in the vicinity of the outer side of the adjacent regionupstream in the scanning direction, a light power of the first lightbeam is increased to be greater than the light energy, engraving along aline segment connecting the fifth point and the sixth point.